To protect your satellites and shoot down enemy missiles. Nearly all aspects of modern life are governed by satellite communication, from military positioning to surveillance to large parts of the entertainment and communications industries. As the Chinese demonstrated, bringing one down is as simple as calculating when it will be flying by and intercepting it with a rocket. The potential for strategic damage to military operations is so great that the U.S. Air Force conducts elaborate space war games, which include scenarios in which the United States loses satellite communication on the battlefield.

Advertisement

Placing nuclear weapons in space has been banned by international treaty since 1967, but the value of placing smaller arms in orbit has been debated ever since. In particular, the notion of using space-based weaponry to intercept ballistic missiles has been on the table since Sputnik, the first man-made object to reach orbit, went up 50 years ago.

In practice, an orbital missile-defense system would be very difficult to set up. Any object flying in low-Earth orbit takes about an hour and a half to make a full circle around the Earth. But a weapons-equipped satellite would have just a few minutes to intercept a nuclear missile on its way to the United States. That means you'd need hundreds of these orbiting weapons to ensure that one of them would be available in the right location at a given time. Researchers at the Union of Concerned Scientists, which opposes space-based weapons, estimate that upward of 1,000 satellite-weapons would be required to get that response time down to three minutes.

According to UCS figures, the United States currently has more than 400 satellites in space, roughly as many as the rest of the world combined. With the region around Earth's gravitational field already cluttered with orbiting debris, it would be difficult to add many more, expenses notwithstanding. Furthermore, the costs of placing a functioning weapon in space are enormous compared with the costs of bringing one down. A system that could attempt to intercept anti-satellite missiles fired from the ground would require a similar network of satellites that would be vulnerable to ground-based attacks.

The continued traction that the idea receives among political and military leaders is usually motivated by fears that the Earth's satellites are largely unprotected. Those on the other side argue that global dependence on satellites makes the prospect of a tit-for-tat orbital shootout extremely unlikely among space-faring nations. That's not to say that rogue nations or terrorists couldn't decide to target orbiting objects with a missile capable of reaching low-Earth orbit. But if they did, virtually all experts say, our best chance of intercepting it would be from here on Earth.